Why is my upload speed significantly higher on a VPN?

I recently purchased a new VPN, and whenever I do that, I run speed tests on the different servers that it provides using speedtest.net.  Throughout all the VPNs I've tested, the upload speed is constantly much higher on the VPN than with my regular connection.  Any ideas on why?  I have an average internet plan, 18 down 1.5 up, (I really wish I had better upload speeds so I could host better servers) and I get about 1.3 to 1.4 without a VPN, but on every VPN in North America I connect to I get around 5mpbs up.  After a quick google search some people suggested that it is due to compression, but I have a hard time believing that I can get my connection over 3 times faster by compressing.  That is with speedtest.net though, I havent ran any FTP tests on real world files yet.  The speedtest.net files might be easily compressed.  Another theroy I have is that the actual VPN server buffers the upload file a little before it starts sending it to the speedtest.net server, or somehow does something weird to bypass my computer and upload directly to the server.  


I thought I should do a real world FTP test, but for some reason my FTP client wouldn't connect.  Using the web client from my hosting company though, I seems to be a lot faster than 1.5mbps (and I was seeding a torrent too).  


What do you think is making it faster, is it just compression?  

I was wondering the same thing although in my case it was a lot more extreme. I pay for 20 Mbps down and 3 Mbps up, but ,when using a VPN that makes my IP address look like my university's, I get 155 Mbps down and 6 Mbps up.